- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Study of the germanium dead layer influence on HP(Ge) detector efficiency by Monte Carlo simulation
摘要： Introduction The dead layer thickness provided by the manufacturer increases with the aging of the HPGe detector; the increase of dead layer thickness leads to the decrease in the detector’s ef?ciency, not only due to gamma rays attenuation in the dead layer but also due to the reduction of the active volume of the detector. Purpose In this work, the dead layer in?uence on HPGe detector ef?ciency was studied by Monte Carlo simulation. Materials and methods The detector model was developed using Monte Carlo N Particle (MCNP5) code for adjustment of the dead layer thickness; the adjustment was performed according to a speci?c irradiation con?guration by collimation approach using three reference point sources: 241Am (59.5 keV), 137Cs (661.6 keV) and 60Co (1173.2 keV; 1332.5 keV). Result The calculated ef?ciencies were compared to the measured intrinsic ef?ciency ones for these point sources; a good agreement between Monte Carlo and measurements results was found after the experimental validation. Conclusion The results con?rm the variation in the dead layer thickness according to aging of the detector; the average change of dead layer is in order of 1.30 ± 0.05 mm after 9 years.
关键词： Dead layer thickness,Detector ef?ciency,Monte Carlo simulation,Point sources,HPGe detector
更新于2025-09-23 15:21:01
-
Photoacoustic imaging for monitoring periodontal health: A first human study
摘要： The gold-standard periodontal probe is an aging tool that can detect periodontitis and monitor gingival health but is highly error-prone, does not fully characterize the periodontal pocket, and causes pain. Photoacoustic imaging is a noninvasive technique that can address these limitations. Here, a range of ultrasound frequencies between 16-40 MHz were used to image the periodontium and a contrast medium based on cuttlefish ink was used to label the pockets. A 40 MHz ultrasound frequency could spatially resolve the periodontal anatomy, including tooth, gum, gingival margin, and gingival thickness of tooth numbers 7-10 and 22-27. The photoacoustic-ultrasound measurements were more precise (0.01 mm) than those taken with physical probes by a dental hygienist. Furthermore, the full geometry of the pockets could be visualized with relative standard deviations of 10% (n = 5). This study shows the potential for non-invasive monitoring of periodontal health with photoacoustic-ultrasound imaging in the dental clinic.
关键词： periodontal disease,gingival thickness,periodontal charting,Photoacoustic imaging,melanin nanoparticles,diagnosis,pocket depth
更新于2025-09-23 15:21:01
-
Geometrical Properties of Spilled Oil on Seawater Detected Using a LiDAR Sensor
摘要： We report on a small-size light detection and ranging (LiDAR) sensor, which offers the possibility of being used in the field during oil spill incidents. In the present study, we develop an algorithm that can distinguish between seawater and oil through the use of a laser at 905 nm wavelength. We investigate the ability of the sensor to detect three different oil types (light crude, bunker A, and bunker C) through experiments and analyze the differences between the types and volumes of spilled oil (1, 5, 10, 15, 20, 25, 30, 35, 40, and 50 mL). The results showed that our algorithm for detecting oil spills over seawater was successful: the LiDAR sensor was able to detect different oil types and volumes. Spilled oil area coverage ranged by more than 50% of the detected area, and the viscosity of bunker C oil reached up to 73%. In addition, the experimental oil spills were mainly formed of oil films of 1 mm and 2 mm thicknesses, which confirmed geometrical properties. Follow-up research should further investigate the characteristics of oil slick thickness measured by the LiDAR system and undertake field tests to assess the feasibility of using the LiDAR system in pollution incidents.
关键词： LiDAR,algorithm,oil spill detection,oil thickness,seawater
更新于2025-09-23 15:21:01
-
Retinal Thickness Changes throughout the Natural History of Drusen in Age-related Macular Degeneration
摘要： SIGNIFICANCE: Drusen are associated with retinal thinning in age-related macular degeneration (AMD). These changes, however, have mostly been examined at single time points, ignoring the evolution of drusen from emergence to regression. Understanding the full breadth of retinal changes associated with drusen will improve understanding of disease pathogenesis. PURPOSE: The purpose of this study was to assess how the natural history of drusen affects retinal thickness, focusing on the photoreceptor and retinal pigment epithelium (RPE) layers. METHODS: Spectral domain optical coherence tomography of subjects with intermediate AMD (n = 50) who attended the Centre for Eye Health, Sydney, Australia, for two separate visits (476 ± 16 days between visits) was extracted. Scans were automatically segmented with manufacturer software then assessed for drusen that had emerged, grown, or regressed between visits. For each identified lesion, the thickness of each retinal layer at the drusen peak and at adjacent drusen-free areas (150 μm nasal and temporal to the druse) was compared between visits. RESULTS: Before drusen emergence, the RPE was significantly thicker at the drusen site (14.2 ± 2.6%) compared with neighboring drusen-free areas. There was a 71% sensitivity of RPE thickening predicting drusen emergence. Once drusen emerged, significant thinning of all outer retinal layers was observed, consistent with previous studies. Drusen growth was significantly correlated with thinning of the outer retina (r = ?0.38, P < .001). Drusen regression resulted in outer retinal layers returning to thicknesses not significantly different from baseline. CONCLUSIONS: The natural history of drusen is associated with RPE thickening before drusen emergence, thinning of the outer nuclear layer as well as photoreceptor and RPE layers proportional to drusen growth, and return to baseline thickness after drusen regression. These findings have useful clinical applications, providing a potential marker for predicting drusen emergence for AMD prognostic and intervention studies and highlighting that areas of normal retinal thickness in AMD may be former sites of regressed drusen.
关键词： spectral domain optical coherence tomography,drusen,age-related macular degeneration,retinal thickness
更新于2025-09-23 15:21:01
-
Focal Relationship Between Structure and Function Within the Central 10 Degrees in Glaucoma
摘要： PURPOSE. To investigate which measurements of inner macular thickness are the most useful for evaluating the focal relationship with visual sensitivity within the central 108 in glaucoma and which layers require correction for retinal ganglion cell (RGC) displacement. METHODS. Sixty eyes of 60 subjects with glaucoma were included. Sensitivity of each test point of 10-2 standard automated perimetry was compared with the thickness of the retinal nerve ?ber layer (RNFL), ganglion cell layer (GCL), GCLt inner plexiform layer (IPL), and RNFLtGCLtIPL (GCC), with and without RGC displacement, using Spearman’s rank correlation coef?cients. Visual sensitivity was evaluated by unlogged 1/Lambert (1/L) values. RESULTS. Retinal nerve ?ber layer thickness correlated signi?cantly with the sensitivities of all test points except for some in the papillomacular bundle region when adjusting for RGC displacement (rs ? 0.287–0.767, P < 0.05). In the central 5.88, the GCL and (GCLtIPL) thickness correlated signi?cantly with the sensitivities of all test points when adjusting for RGC displacement (GCL: rs ? 0.363–0.729, P < 0.01; (GCLtIPL): rs ? 0.359–0.715, P < 0.01). The GCC thickness correlated signi?cantly with the sensitivities of all 68 test points when adjusting for RGC displacement (rs ? 0.359–0.767, P < 0.01). RGC displacement improved the correlation between sensitivity and GCL, (GCLtIPL), and GCC in the central 4 points (GCL: rs ? from 0.270–0.470 to 0.421–0.540; (GCLtIPL): rs ? from 0.195–0.450 to 0.381–0.549; GCC: rs ? from 0.132–0.449 to 0.359–0.562). CONCLUSIONS. The GCC is the most useful parameter to evaluate structure and function within the central 108 in glaucoma. Adjusting for RGC displacement is essential to evaluate the relationship between structure of the GCL-related layer and function at the central macula.
关键词： focal relationship,RGC displacement,visual sensitivity,inner macular thickness
更新于2025-09-23 15:21:01
-
Reproducibility of Central Corneal Thickness Measurements in Normal Eyes Using the Zeiss Cirrus 5000 HD-OCT and Pentacam HR
摘要： Objectives: To determine the repeatability and reproducibility of Central Corneal Thickness (CCT) measurements using two different anterior segment imaging modalities, including those obtained with the new anterior segment lens attachments for the Cirrus 5000 HD-OCT. Methods: A total of 32 eyes from 16 normal volunteers (8 male, 8 female) were enrolled in this prospective study. CCT was measured by the same examiner using the Cirrus 5000 HD-OCT and Pentacam HR. The results of CCT obtained by each method were averaged and compared using t-test analysis. The agreement between the measurement methods was evaluated. Coefficient of Repeatability (CoR) and Intra-Class Correlation Coefficient (ICC) were computed. Results: The mean measurements taken with the Cirrus OCT anterior chamber lens (CCTAC), HD cornea lens (CCTHDC) and pachymetry scans (CCTPach) were 545.35 ± 31.02, 537.87 ± 26.82, and 532.04 ± 29.82 μm, respectively. The mean CCT obtained with the Pentacam (CCTPent) was 545.51 ± 30.71 μm. CCTPent were significantly higher than CCTHDC and CCTPach (p< 0.0001). In contrast, the CCTPent and CCTAC were similar (p=0.87). CCT, as evaluated by the two different instruments, showed excellent correlation (r > 0.98, p< 0.0001) with an ICC > 0.99 (95% CI, 0.97 – 0.99). CoR was the highest for CCTPach (3.7 ± 1.4, 95% CI (3.0- 4.6)). Conclusion: CCT measurements from the Cirrus OCT using the new anterior segment lens attachments and the Pentacam HR are highly correlated. This should allow the use of a standardized correction factor if necessary to inter-relate the measurements between the two devices.
关键词： Imaging,Central corneal thickness,Cornea,Optical coherency tomography,Scheimpflug technology,Pachymetry
更新于2025-09-23 15:21:01
-
Effect of Molecular Weight of Polyethylene Glycol on the Sheet-thickness and Photocatalytic Performance of MoS2 Nanoparticles
摘要： Molybdenum disulfide (MoS2) nanomaterials have attracted considerable attention recently owing to its unique photoelectrochemistry property and promising applications in the conversion of solar energy to chemical energy and environmental purification. Flower-like MoS2 photocatalyst was synthesised via hydrothermal method in this work. To achieve the MoS2 nanoparticles with various sheet-thickness, polyethylene glycols (PEG) with deferent molecular mass were employed as additives in the preparation process. The effects of the molecular weight of PEG on the micro structure and crystal structure of MoS2 nanoparticles were characterized by field emission scanning electron microscopy (FESEM), high resolution transmission electron microscope (HRTEM) and X-ray diffraction (XRD). The photocatalytic properties of as-synthesized products were evaluated by the degradation of methylene blue (MB) under ultraviolet irradiation. The results suggest that the molecular weight of PEG could affect the sheet thickness of the MoS2 particles. In addition, the degradation rate of MB show that the photocatalytic performance of MoS2 nanoparticles is closely related to their sheet thickness, the photocatalytic activity reduced with the decrease of sheet thickness of MoS2 nanoparticles which is mainly attributed to the reduction of the active sites.
关键词： Photocatalytic performance,MoS2 nanoparticles,Hydrothermal method,PEG,molecular weight,Sheet-thickness
更新于2025-09-23 15:21:01
-
Study and Calculation Electrical Properties of Silver Thin Layers by Four- Point Probe Method
摘要： In this research Ag thin layers on silicon p-type substrate with crystal orientation (100) and 300, 360 and 400 nm thicknesses by thermal evaporation was deposited. Four-point probe and XRD analysis of surface layers consequently for study electrical properties included of sheet resistance, conductivity, resistivity and investigation of Ag phase formed, was done. As result XRD was shown that at 400 nm the best state of silver face-central cubic (FCC) structure with crystal orientation (200) was formed and by Deby-Scherrer formula distance between successive plates was calculated 8.94 nm. Four-point illustrated that sheet resistance and electrical resistivity with increase thickness, decreases while conductance increases. At 400 nm thickness Ag layer has the most conductivity and the lowest resistance.
关键词： FCC lattice,Thickness,Sheet Resistance,Conductivity
更新于2025-09-23 15:21:01
-
Changes in Retinal Layer Thickness in the?Contralateral Eye of Patients with Unilateral Neovascular Age-Related Macular Degeneration
摘要： To evaluate the thickness of the outer retinal layers and its relationship with visual function in fellow eyes of participants with unilateral neovascular age-related macular degeneration (AMD). Design: Longitudinal study. Participants: We enrolled 105 subjects with unilateral neovascular AMD from 3 clinical centers in Europe. Methods: The fellow eye, without advanced AMD, was selected for the study. Subjects were followed up with visits occurring every 6 months for 2 years. Spectral domain optical coherence tomography volume scans were collected at 3 clinical sites, in Belfast, Northern Ireland; Coimbra, Portugal; and Milan, Italy. Detailed manual segmentation of outer retinal layers was performed using the custom-designed and validated grading software 3D OCTOR. Thickness measurements for neurosensory retina, photoreceptor layer (PRL) outer segments, retinal pigment epithelium plus drusen (RPEtdrusen) complex, and choroidal layers from each sector of the standard macular grid were obtained. Measures of vison were distance visual acuity, near visual acuity, Smith-Kettlewell Institute low-luminance acuity score, and reading speed. Subjects were grouped based on the presence or absence of subretinal drusenoid deposits (SDDs) for further analysis. Main Outcome Measures: Change in thickness of retinal layers and change in measures of vision. Results: In all, 85 eyes were included in the analysis. The average duration of follow-up was 20.5 (cid:2) 5.8 months. By the ?nal visit, the RPEtdrusen complex was signi?cantly thinner when compared with baseline (29.7 mm vs. 34.09 mm; P ? 0.03). Low-luminance de?cit was signi?cantly worse at the ?nal visit (P < 0.001) and correlated with PRL outer segment thickness (r ? 0.33; P ?0.02). The RPEtdrusen complex was signi?cantly thicker in eyes with SDDs compared with that in those without SDDs (30.67 mm vs. 28.64 mm; P ? 0.02). PRL outer segments became signi?cantly thinner over time in eyes with SDDs compared with those in eyes without SDDs. Conclusions: The RPEtdrusen complex layer becomes thinner over time in fellow eyes of subjects with unilateral neovascular AMD. The rate of PRL outer segment thinning was higher in eyes with SDDs than in eyes without SDDs. These ?ndings are preliminary steps in the identi?cation of early biomarkers for detecting and monitoring the progression of AMD. Ophthalmology Retina 2018;-:1e10 a 2018 Published by Elsevier Inc. on behalf of the American Academy of Ophthalmology
关键词： spectral domain optical coherence tomography,visual function,retinal layer thickness,subretinal drusenoid deposits,age-related macular degeneration
更新于2025-09-23 15:21:01
-
Preparation and characterization of carbon nanotubes by pulsed laser ablation in water for optoelectronic application
摘要： In the present work, preparation of multi-walled carbon nanotubes (MWCNTs) and carbon nanoparticles (CNPs) by using pulsed laser ablation of a graphite target in water without using catalyst was demonstrated. The effect of laser wavelength on the optical absorption and structural properties has been studied. X-ray diffraction (XRD) data shows the synthesized CNTs were polycrystalline and a peak related to the diamond structure was observed. Scanning electron microscope (SEM) investigation displays that the average diameter of CNTs synthesized with 532 nm was 20 nm and few micrometers in length, while the CNTs synthesized with 1064 nm have an average diameter of 75 nm and lengths of few sub-micrometers. Some of CNPs were noticed to deposit on the CNTs. Transmission electron microscope (TEM) was used to study the morphology of MWCNTs. Raman spectra confirm formation of MWCNTs during the presence of three peaks belonged to D-band, G-band and 2D-band. The intensity ratio of IG/ID is larger than unity for MWCTs prepared by two laser wavelengths. The colloidal MWCNTs prepared by 532 nm laser pulses showed higher absorption than that of MWCNTs prepared with 1064 nm. The current-voltage characteristics and responsivity of hybrid In/p-MWCNTs/n-Si heterojunction photodetectors prepared at different CNTs film thicknesses were investigated at room temperature. The responsivity of hybrid MWCNTs/n-Si photodetector has two peaks of response, the first peak was found at 650 nm and the second peak located at 850 nm. The maximum responsivity was 0.53 A/W at 532 nm was found for the photodetector fabricated with 532 nm laser. The energy band diagram of MWCNTs/Si heterojunction was constructed under illumination condition.
关键词： Hybrid photodetector,CNTs,Laser ablation,CNTs thickness,Laser wavelength
更新于2025-09-23 15:19:57